Automatic strip thickness control apparatus



Feb. 21, 1961 J. w. WALLACE ET AL 2,972,268

AUTOMATIC STRIP THICKNESS CONTROL APPARATUS Filed April 8, 1957 3Sheets-Sheet 2 350m muuto 0 o :00 250 z mu m tcoo 8 2 mm! 6: 0 czouamcummm 350w ww h m mm 8 mm 12 N L .0.Q 0 4 Feb. 21, 1961 w WALLACE ETAL2,972,268

AUTOMATIC STRIP THICKNESS CONTROL APPARATUS Filed April 8, 1957 3Sheets-Sheet 3 D. 0. Voltage I Source A. 0. Voltage Source D. C. VoltageSource A.g.Voltoqe ource Input VD Output Fig. 4

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United States Patent AUTOMATIC STRIP THICKNESS CONTROL APPARATUS John W.Wallace, Orchard Park, and Robert E. Hull, Amherst, N.Y., and Raymond W.Moore, Whitehall, Pa., assignors to Westinghouse Electric Corporation,East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 8, 1957,Ser. No. 651,387 14 Claims. (Cl. 80-32) The present invention relates,in general, to control apparatus for automatically controlling theoperation of one or more motor devices, and more particularly, relatesto automatic control apparatus for controlling the gauge or thickness ofa strip of material by controlling the operation of one or more motordevices of a rolling mill operative to determine the gauge or thicknessof a continuous strip of metal or other material.

It is an object of the present invention to provide improved motorcontrol apparatus, and more particularly, to provide improved apparatusfor controlling the operation of one or more motor devices of a striprolling mill or the like, to thereby better control the final gauge orthickness of the strip over a greater portion or length of said strip. a

It is another object of the present invention to provide improvedcontrol apparatus for a strip rolling mill, which apparatus is morerapidly responsive to any deviation in the operation of said rollingmill away from a predetermined operation or a reference operation, suchas a strip thickness determination, and further, to provide improvedapparatus which is capable of more rapidly correcting for and removingany such deviation in the operation of said rolling mill to therebyimprove the operating efliciency regarding the on-gauge or desiredthickness of strip as the final product.

It is a different object of the present invention to provide improvedcontrol apparatus for a strip rolling mill, which apparatus is operativeto better control the strip thickness by varying the tension of thestrip relative to one or more stands of the rolling mill, and further,to provide improved apparatus operative to vary the spacing between theroller members of one or more stands of the rolling mill as necessary tobetter control said strip thickness for errors in thickness greater thana predetermined magnitude, and to thereby prevent strip breakage orstrip sagging due to the otherwise required excessive strip tensionvariation.

It is a further object of the present invention to provide improvedcontrol apparatus operative with a strip rolling mill for better holdingsubstantially constant or as may be desired the pressure between thecooperating roller members of one or more stands of the rolling mill tothereby better control the spacing between said roller memberssubstantially constant or as may be desired.

It is an additional object of the present invention to provide improvedcontrol apparatus for better controlling the output strip thickness orgauge from a strip rolling mill which apparatus is operative toautomatically reset the control apparatus from a first screw-downsetting condition to a second screw-down setting condition should anoperator change to said second screw-down setting condition ofoperation.

The use of well known X-ray or radiation type of thickness gauges as athickness error detection device presents two major problems. Firstly, atransport time delay is introduced, consisting of the time required fora given section of the strip to pass from the roller members to thethickness sensing gauge. The latter gauge must be positioned about 6 or7 feet from the roller members, and thusly an immediate sensing ofthickness errors cannot be made in this manner. Also stability problemsare introduced into the strip thickness control apparatus by thisdevice. Secondly, radiation type gauges are relatively complex andsensitive instruments that are difiicult to adjust, have rather lowpower output signals, and generally have an inherent time delay providedby the gauge itself. Thusly, only a limited strip thickness controlaccuracy is obtainable as a result of this time delay and the noiselevel of the thickness gauge.

These and other objects and advantages of the present invention willbecome apparent in view of the following description taken inconjunction with the drawings, wherein:

Figure 1 is a diagrammatic showing of one form of the control apparatusin accordance with the teachings of the present invention;

Fig. 2 is a schematic showing of the subject control apparatus;

Fig. 3 is a curve chart illustrating the operation of the subjectcontrol apparatus;

Fig. 4 is a schematic showing of magnetic amplifier devices connected ina push-pull circuit arrangement suitable for use with the presentcontrol apparatus;

Fig. 5 is a schematic showing of a well known limiter circuitarrangement suitable for use with the present apparatus; and

Fig. 6 is a schematic showing of a well known deadzone circuitarrangement suitable for use with the screwdown control device ifdesired.

In Fig. 1 there is shown control apparatus for a ro ling mill includinga mill stand 10 having an upper roller member 12 and a lower rollermember 14 between which a strip of material 16 may be positioned, suchthat the spacing between the upper roller member 12 and the lower rollermember 14 is effective to determine the thickness or the gauge of thestrip of material 16 after it has passed from the previous mill standthrough the stand 10 to a successive stand or the delivery reel 20. Ascrew-down control device 22 is operated by a suitable motor 24controlled by a screw-down control device 25 for determining saidspacing between the upper roller member 12 and the lower roller member14.

The operative speed of the stand 10 is determined by a motor 26 operatedby a motor control device 28 which, in turn, is responsive to a controlsignal from a strain gauge device 30 mounted on the mill stand 10 andresponsive to the pressure between the upper roller member 12 and thelower roller member 14, as reflected by strain induced in the housing ofthe mill stand 10, and thereby the spacing between said roller members.The strain gauge device 30 provides a control signal to a firstamplifier device 32 which, in turn, provides this amplified controlsignal to a second amplifier device 34, and to an integration device 36which, in turn, provides a control signal to the amplifier device 34.The resultant output signal from the amplifier device 34 is supplied tothe motor control device 28 for controlling the operation of the millmotor 26 in accordance with a control signal received from the straingauge 30. If this resultant control signal has a value greater than apredetermined value, a control signal is supplied to the screw-downcontrol device 25.

In Fig. 2 the rolling mill stand 10 is shown including the upper rollermember 12 and the lower roller member 14'. A first strain gauge 31 ismounted on one side of the mill stand housing 10 and a second straingauge 33 is mounted on the opposite side of the mill stand housing 10.Differential type transformer strain gauges may also be used. The straingauges are mounted in diametrically opposite posts of the mill housing.Any well known type 3 of strain gauge, such as a resistance elementgauge, may be used. The first strain gauge 31 is operative with acontrol winding which has an inductance value varied as a function ofthe strain within the mill stand housing as sensed by the strain gauge31. The second strain gauge 33 is operative with a control winding 42which-has an inductance value which varies as a function of the strainin the mill stand housing as sensed by the strain gauge 33;

The control windings 40 and 42 are connected in a bridge circuit withreference windings 43 and 46 and energized by a suitable alternatingcurrent voltage source 48, such that any unbalance of the latter bridgeresulting from physical strain in the housing of the mill stand 10 assensed by either or both of the strain gauge devices 31 or 33 isoperative to provide to the alternating current terminals of a rectifierbridge device 50 a control signal which varies in accordance with saidstrain in the mill stand housing. The direct current terminals of therectifier bridge 5i} are connected through conductors 52 and 54 to thecontrol windings 56 and 58 of a magnetic am-' plifier device to therebyenergize said control windings 56 and 58 with a direct current signalwhich varies as a function of the spacing between the upper rollermember 12 and the lower roller member 14 which, in turn, is a functionof the roll pressure or roll force as applied to the strip 16.

A second pair of control windings 60 and 62 are energized from a signalfrom across a pressure reference setting potentiometer 64 as determinedby the setting of a movable contact arm on said potentiometer 64 as willbe later explained. The pressure reference setting potentiometer 64 ispart of a bridge circuit including a direct current voltage source 66which energizes a potentiometer 68 operative to vary the range segmentof the pressure reference potentiometer, in other words, operative as acoarse setting for the pressure reference setting potentiometer 64. Avernier setting potentiometer 70 is connected in series with thepotentiometer 64.

The output load windings of the magnetic amplifier device 81) areconnected in a push-pull arrangement across the impedance devices 82 and84 toprovide a voltage drop across said impedance devices 82 and 84having a magnitude which varies as a function of the magnitude of theroll force or pressure between the roller members 12 and 14 and whichhas a polarity determined by the actual pressure between the rollermembers 12 and 14 being either above or below a predetermined referencepressure as determined by the pressure reference setting potentiometer64. The control voltage signal across the impedance devices 82 and 84 isapplied to the control windings 36 and 88 of a second magnetic amplifierdevice 90. This same control voltage is applied through conductors 92and 4 to the control windings 96 and 98 of a third amplifier device 100,of the integration device 36. A sec- 0nd pair of control windings 102and 104 of the amplifier device )6 is energized by a control signalreceived from the integration device 36 as will be'later described.

The output or load windings of the amplifier device are connected in apush-pull arrangement across the impedance devices 108 and 110, with theoutput. control signal across the latter said impedance devices 108 and111 being applied to the control windings 112 and 114 of a magneticamplifier device 116 within the motor control device 28.

The output control voltage from across the impedance devices 108 and isalso applied across a first pair of control windings 118 and 120 of theamplifier device 169. A second pair of control windings 122 and 124 aswell as a third pair of control windings 126 and 128 are energized asfeedback stabilization windings by the voltage difference between thecontact arms of the respective potentiometers 130 and. 132 of a bridgecircuit energized by a suitable direct current voltage source 134, asshown in Fig. 2. A servo or reset motor 136 having a forward fieldwinding 138 and a reversecontrol field winding 140 is energized by theoutput or load windings of the amplifier device 100, with the resetmotor 136 being operatively connected through the clutch device 146 tothe contact arm of the potentiometer 132.

The control windings 1412 and 104 of the amplifier device 90 areenergized through the conductors 148 and 150 by a signal determined bythe settings of the respective contact arms of the potentiometer devices130 and 132.

The output or load windings of the amplifier device 116 of the motorcontrol device 28 shown in Fig. l, energizes the impedance devices 152and 154 which, in turn, energize impedance devices 156 and 158 connectedin a series reference circuit. The latter series reference circuitfurther includes the impedance devices 160 and 162 which receive throughthe operation of the amplifier device 164 and the impedance device 166an IR compensating feedback control signal. Also a reference excitationgenerator 168 is provided having a control field 170 energized by asuitable direct current voltage source 172. A supply generator 174 isprovided for controlling the energization of the mill motor 26 and, inturn, i11- eludes control field windings 176 and 177 energized by anamplifier device 178. The control windings 180 and 182 of the latteramplifier device 178 are connected in the above series reference circuitalong with the first pair of impedance devices 156 and 158 provided witha thickness error correction signal and the second pair of impedancedevices 166 and 162 provided with an IR compensating feedback signal andthe reference excitation generator 168 and the energy supply generator174. Thusly, the control windings 181 and 182 are operative through theamplifier device 178 to control the energization of the control fieldwindings 176 and 177 of the supply generator 174 to thereby control theoperating speed of the mill motor 26 and thusly, the speed of the millstand 10 to thereby vary the tension of the strip 16 as may be desiredto correct for any errors in the thick ness or gauge of the strip 16, ascompared to a predetermined desired gauge or thickness for the strip 16.

In Fig. 3 there is shown a curve chart illustrating the operation of thecontrol apparatus in accordance with the present invention. In Fig. 3there is a plot of delivery strip thickness or gauge deviation as afunction of the length of the strip of material. The initial threadingof the strip through the rolling mill and the start-up operationnormally causes an initial length or portion of the strip which is noton gauge as shown by the dotted portion of the curve, then the remainingportion of a particular coil of the strip may be on gauge up to aportion between coils where the ends of the successive coils are weldedor fastened together which may not be on gauge as shown by the dottedcurve portion, then a second potrion of the total length of the strip ison gauge until the end of the last coil where the mill operation mustslow down and stop.

With the control apparatus of the present invention, this initialthreading and start-up portion of the strip or at least a considerableportion of this initial part of the strip may be made to be on gauge asshown by the solid curve portion, as is asubstantial portion of thein-between or welded segment of the strip and the final segment of thestrip.

In Fig. 4 there is shown a schematic showing of a push-pull circuitarrangement using magnetic amplifier devices, and suitable for-use inthe subject control apparatus. In the schematic circuit of Fig. 3, theoutput terminals of the load windings of the magnetic amplifier deviceshave been shown, and not the load winding as such, in an effort tosimplify the illustration of the drawing. However, it should beunderstood that the load winding circuits including the unidirectionalconductive devices as shown in Fig. 4 are intended to be used.

In Fig. 5 there is illustrated a well known limiter device,

operative such that when the voltage applied across the input terminalsA and B is greater than the voltage provided by the adjustable DC.voltage source across the bridge terminals C and D, a low impedance pathfor any difference voltage is provided in parallel with any output orload device connected to the output terminals.

In Fig. 6 there is shown a well known dead zone or dead-band device,operative such that when the voltage across the input or terminals A andB of the bridge is less than the voltage provided by the adjustable DCvoltage source across the terminals C and D of the bridge device, nocurrent will flow to a load device connected across the outputterminals.

In accordance with the operation of the subject control apparatus thezero setting of the potentiometer device 132 within the integrationdevice 36 may be initially made by closing the clutch device 65connecting the movable contact arm of the pressure reference settingpotentiometer 64 with the reset motor 136 and opening the clutch device146 to disconnect the contact arm of the potentiometer device 132 fromthe reset motor 136. For the initial reset or zero error settingoperation, the conductor members 92 and 94 are operative to sense anythickness error control signal received from the strain sensing device31 and strain sensing device 33 when the roller members 12 and 14 arespaced in accordance with the predetermined and desired strip thickness,and is operative to control the operation of the reset motor 136 throughthe clutch device 65 to move the contact arm of the potentiometer 64 tobalance out any such error voltage by suitably energizing the controlwindings 60 and 62 such that a zero control voltage or signal is thereby provided across the impedance devices 82 and 84. In this regard, thecontact 95 is initially closed for the zero control reset operation andthe contacts 97, 99 and 101 are initially open. Now, the clutch member65 is opened and the clutch member 146 is closed to thereby disconnectthe contact arm of the potentiometer 64 from the reset motor 136 and toconnect the contact arm of the potentiometer 132 to the reset or servomotor 136. Additionally, the contact member 95 is opened and the contactmembers 97, 99 and 101 are closed such that now the control apparatus isreadied for the normal operation of the mill stand relative tocontrolling the thickness or gauge of the strip 16.

The initial zero setting should be made with the strip 16 between theroller members 12 and 14 at the predetermined desired thickness of thestrip 16 or with the predetermined desired spacing between the upperroller member 12 and the lower roller member 14.

Now with the mill stand ready for normal operation with the strip 16passing between the upper roller member 12 and the lower roller member14, the strain gauges 31 and 33 are operative to sense the pressurebetween the roller members and to provide an output signal across theimpedance members 108 and 110 in the output of amplifier device 90 inthe form of an error correction signal. This error correction signal issupplied through the now closed contactor 101 to the control windings118 and 120 of the amplifier device 100 to control the energization ofthe load windings to suitably control the operation of the servo motor136 through the now closed clutch 146 to move the position of thecontact arm of the potentiometer 132, such that a difference vo'ztagehaving a magnitude corresponding to the difference between the actualroll pressure as sensed by the strain gauges 31 and 32 and thepredetermined desired roll pressure as provided by the potentiometer 64through the control windings 60 and 62 of the amplifier device 80, and apolarity determined by the actual roll pressure being greater or smallerthan said predetermined reference is provided, which error or differencesignal in the form of an integrated signal is applied through theconductors 148 and 150 to the control windings 102 and 104.

The error control voltage is thusly reduced to zero by the operation ofthe latter integration signal applied to the integration controlwindings 102 and 104.

In this respect the control by the present apparatus of the operatingspeed of the mill stand motor 26 or the control of the screw-down motor24 is intended to be an initial and very rapid correction with thecorrection subsequently being handled by the radiation gauge 190 inaccordance with the teachings of copending application Serial No.651,512, filed April 8, 1957, by the same inventors as the presentapplication and assigned to the same assignee, and further, inaccordance with the teachings of copending application Serial No.651,386, filed April 8, 1957, by the same inventors and assigned to thesame assignee.

The operation of the strain gauges 31 and 32 is to sense the actualpressure or force between the upper roller member 12 and the lowerroller member 14 and to thereby vary the impedance relationship of thebridge circuit including the variable impedance members 40 and 42 toenergize the control windings 56 and 58 of the amplifier device with acontrol signal in accordance with the actual roll pressure or forcebetween the roller members of the mill stand 10. The control windings 60and 62 receive a predetermined energization in accordance with apredetermined desired roll pressure corresponding to a predeterminedspacing between the roller lmernbers, and thereby a predeterminedthickness or gauge of the strip 16. Any difference between theenergization of the reference control windings 60 and 62 and the actualpressure energization of the control windings 56 and 58 results in adifference control signal or error correction control signal beingapplied across the impedance members 82 and 84 and, in turn, passesthrough the control windings 86 and 88 of the succeeding amplifierdevice 90 to result in an error correction control signal appearingacross the impedance devices and 108. The error correction controlsignal from across the latter impedance members 108 and 110 is appliedto the control windings 112 and 114 of the output amplifier device 116for varying the operative speed of mill motor 26 and is secondly appliedto the control windings 118 and 120 of the reset amplifier device 100 tocause the reset motor 136 to operate in a direction in accordance withthe polarity of the error correction control signal and to operate anamount or to reset the control arm of the potentiometer device 132 anamount corresponding to the integral of the error correction controlsignal, to thereby provide a feedback or integration control signal tothe control windings 102 and 104 to balance out or bring to zero theerror correction control signal resulting from the difference betweenthe actual roll pressure and the predetermined desired roll pressure.

In this respect the operation of the integrator device 36 is slow actingand thereby, is operative to correct for a major portion of the initialerrors in strip thickness and allows the radiation gauge after apredetermined transmit time from the mill stand 10 to detect the gaugeor thickness error and provide the desired subsequent and more accuratecorrection to either the mill motor 26 or the screw-down motor 24 inaccordance with the above-described copending applications.

In the operation of the control apparatus in accordance with the presentinvention, it is desirable to hold the gauge or thickness of the strip16 to within one-tenth of a mil accuracy, in other words to within oneten-thousandths of an inch accuracy. The output signal from the straingauge devices 31 and 33, including their respective variable inductancecontrol windings 40 and 42, is a voltage proportional to the actualrolling pressure between the roller members 12 and 14, which controlvoltage is applied to the control windings 56 and 58. This actualrolling pressure is equal to the predetermined desired pressurecorresponding to the predetermined desired thickness or gauge of thestrip 16 plus or minus any change in the rolling pressure due to anyerror in the gauge'or thickness of the strip. Thusly, the pressurereference potentiometer 64 is operative to energize the control windings6t and 62 to balance out the voltage re ceived from the strain gaugedevices corresponding to the desired rolling pressure, such than anyoutput signal from the amplifier device 80 as applied to the impedancemembers 82 and 84 corresponds to the change in roll pressure due to anyerror in the gauge or thickness. When the impedance members 82 and 84have no voltage drop across them, this corresponds to an operatingcondition of the mill stand with the actual gauge or thickness of thestrip 16 corresponding to the predetermined desired gauge or thickness.

Thusly, any error correction control signal across the impedance members82 and 84 is applied through the impedance members res and 110 to thecontrol windings 112 to 114 to vary the output voltage of the generatordevice 174, and to thereby vary the tension of the strip 16 relative tothe mill stand 10 by correspondingly varying the operating speed of themill motor 26 and thereby the operating speed of the mill stand 10.

The control apparatus in accordance with the present invention must havea strip thickness error condition to provide an output signal across theimpedance members .108 and lit The amplifier device 1% senses any erroroutput voltage across the output of the amplifier device 90 and movesthe reset motor 136 to supply to the control windings 102 and iii -5- ofthe amplifier device 9% an integrated signal to cancel out the errorcorrection signal received from the amplifier device 89, thusly, causingthe output of the amplifier device 96 to go to zero slowly. In thisrespect, the integration device 36 is operative to cancel out the errorcorrection signal in the output of the amplifier device 90 in a timeperiod of from 1 to 2 seconds. This allows the radiation gauge 1% andits associated control apparatus in accordance vwith the teachings ofthe above-copending applications to follow with the needed subsequentgauge or thickness corrections to thereby replace the error correctingaction of the strain gauge control system in accordance with the presentapplication.

If the operator of the rolling mill, including the mill stand 10, shoulddecide to jog the screw-down device 22 to thereby jog or vary thespacing between the roller members 12 and 214, for example, betweensuccessive rolls or coils of strip, the screw-down device 22 isoperatively connected, by relay devices not shown but well known topersons skilled in this art, with the clutch members 65 and 146 and withthe contact members 95, 97 and 101 to close the clutch 65 and open theclutch 146 and to close the contact 95 and to open the contacts 97, 99and 101, such that the reset motor 136 operates to fast calibrate theposition of the contact arm of the potentiometer 64 through the clutchmember 65 to provide a new reference control signal to the controlwindings 6t) and 62 of the amplifier device 86 to balance out the errorsignal received from the strain gauges 3i and 33 to thereby provide theamplifier device 55% with the desired zero output voltage signal andthereby recalibrate the control apparatus to the new roll pressureas-sensed by the strain gauges 31 and 33 and corresponding to the newpredetermined desired roll pressure.

if the end of a particular coil of strip material occurs with an errorin the strip gauge present as sensed by the strain gauges 3i and 33, andthusly, providing an error corrective control signal across theimpedance members 158 and 110, this same corrective control signal maynot be needed for the next succeeding coil. Thusly, the bridge includingthe potentiometer devices 130 and 132 has its output voltage measuredthrough the contactor 97 to reset the potentiometer 132 and to therebycancel any prior corrective action. in this respect, the contactor 97closes at the end of the coil, by relay devices not shown, and thecontactors 9 and 1191 open at the end of a coil to cancel any priorcorrective actionby resetting the contact arm 132 of the potentiometerdevice by suitably con trolling the resetmotor 136 to a zero or balanced,condition.

The slow integration operation is desirable because of temperaturechanges, in the mill housing or oil film thickness on the mill rollerbearings. Otherwise, a gauge error may be indicated falsely clue tothese conditions which would not be detected until the radiation gauge190 was operative after, the time lag due to the passage of theparticular section of strip from the mill stand it) to the radiationgauge 1%. In this respect, the strain gauge control apparatus inaccordance with the teachings of the present application is intended tobe operative relative to the predetermined and desired strip thicknessand to correct for changes in strip gauge or thickness, whereas theradiation gauge control apparatus in accordance with the teachings ofthe copending application Serial No. 651,386, filed April 8, 1957, isintended to be operative relative to the actual gauge or thickness ofthe strip,

Further, it, should be noted that any time that the screw-down device 22is jogged by the control motor 24, whether the mill stand Ill isoperating or not, the clutch device 65 will close and the contact member95 will close to sense the output of the amplifier device 86 and operatethe reset motor 136 to recalibrate the position of the contact arm onthe potentiometer 64 as may be desired to zero the output signal fromthe amplifier device 80.

The operation of the subject strain gauge apparatus is such that itreceives an immediate indication of gauge or thickness error bymeasuring the rolling pressure of the mill stand ltl between the upperroller member 12 and the lower roller member 14 and thusly, the roll gapopening. The strain gauge system is fundamentally operative to holdsubstantially constant the rolling pressure in a predetermined millstand such as the fifth mill stand. Holding a substantially constantrolling pressure is operative according to Hookes law, such that thestretch of the mill stand is substantially proportional to the strain orroll pressure up to the elastic limit of the mill stand and the elasticconstant of the mill housing rolls, and in this manner a constant rollgap may thereby be efiected. As there is little or no elastic recoveryof the strip in a cold mill, the roll gap opening is also a measure ofthe delivery gauge or thickness.

In the operation of the subject strain gauge control system, a magneticstrain gauge 30 is mounted on one or more of the fifth stand columns anda signal proportional to the actual rolling pressure is continuously andimmediately obtained. The amplifier device 84 is operative to build upthe power level and the voltage level of this actual rolling pressuresignal and the output of the amplifier device is fed into a secondamplifier device fit) which is operative to further increase the signallevel.

The output of the latter amplifier device 90 is fed into the fifth standamplifier device 116 in exactly the same manner as, and additive to, theerror correction control signal from the radiation gauge control systemas described in the above copending application Serial No. 651,386,filed April 8, 1957.

To provide an error correction control signal from the output signalreceived from the strain gauge 30, which may include the two straingauges 31 and 33 shown in Fig. 3, a reference signal is provided andsupplied to one set of control windings of the amplifier device 80. Thedifference between the strain gauge output signal and this latterreference signal represents the error correction signal and appears atthe output of the amplifier device 80.

According to Hookes law whenever the screw-down device 22 is operated tochange the screw-down or specing between the roller members and it isdesired to roll the same strip gauge or thickness as was being rolledprior to said screw-down change, a new rolling pressure must be used.Therefore, the reference voltage received from the potentiometer member64 must be re- 9. calibrated and is so recalibrated automatically by theoperation of the screw-down control device 25 whether the screw-downjogging is done automatically or manually.

The integration device 36 is operative as a slow integrate device duringnormal running of the mill stand above threading speed with the unitbeing responsive to the output error correction signal of the secondamplifier device 90 and slowly causes this output error correctionsignal to go to zero by inserting a differential control signal into thecontrol windings 1G2 and 104 of the amplifier device 90. The latteraction is provided mainly to guarantee that any possible drift orunwanted change in roll gap due to temperature changes or oil filmthickness on the bearings for the roller members 12 and 14, rather thandue to changes in incoming strip variations, Will be cancelled out andthe reference will be recalibrated for these former changes. In thisregard, the radiation gauge 190 is operative as the ultimate standard ofmeasurement of delivery gauge or thickness under all conditions of millstand operation.

At the finish of a roll or coil of strip and previous to running thesuccessive coil, the integrator bridge including the potentiometermembers 130 and 132 is zeroed so that it cannot insert an unwantedsignal when starting the next run on a successive strip of material.Also, during this change-over period or if the screws are jogged duringnormal running operation, the pressure reference is reset to the valuedesired by the operator.

It should be understood that the subject control apparatus senses theactual rolling pressure between the roller members. If, for example, theactual strip thickness at the roller members is too thick, thisincreases the actual rolling pressure, and causes thesubject controlapparatus to provide an error correction signal having a polarity, forexample positive, for increasing the speed of the roller members tothereby increase the strip tension relative to the roller members andthereby effecting an increased strip thickness reduction by the rollermembers and in this manner return to the desired rolling pressure. Inthis regard it should be understood that either entry strip tension ordelivery strip tension relative to the roller members may be varied asdesired for strip thickness error correction. However, relative toparticularly the final stand of the rolling mill, it may be preferableto vary entry strip tension and not interfere with the desired stripcoiling operation by the delivery winding reel. 7 It should be furtherunderstood that the teachings of the present application, as well as theteachings of the referenced copending applications, are readilyadaptable to single or multiple stand mills, either tandem or reversiblemills. Also it should be understood that the subject strip thicknesscontrol apparatus is intended to be added to or combined with thepresently well known rolling mill control apparatus for the mill standsand winding reels as well known to persons skilled in this art.

Although the present invention has been described with a certain degreeof particularity, it should be understood that the present disclosurehas been made only by way of example and that numerous changes in thedetails of construction and the combination and arrangement of parts maybe resorted to without departing from the scope and the spirit of thepresent invention.

We claim as our invention:

1. In control apparatus for a rolling mill including a first devicehaving a pair of roller members between which a strip of material may bepositioned for performing a predetermined operation relative to saidstrip of material, withsaid rolling mill including a second device forpulling on the strip relative to said first device, the combination of aroller pressure sensing device for providing a first control signal thatvaries as a predetermined function of the roll pressure between saidpair of roller members, a motor member operative with one of said firstand second devices for controlling the tension in said strip betweensaid first and second devices, a first motor control device responsiveto said first control signal and operatively connected to said motormember for controlling the tension of s'aid strip between said firstdevice and said second device in accordance with the variations of saidfirst control signal, and a second motor control device responsive tosaid first control signal for providing a second control signal thatvaries as a predetermined function of the variations of said firstcontrol signal, with said first motor control device being responsive tosaid second control signal for controlling the tension of said stripbetween said first device and said second device in accordance with thevariations of said second control signal.

2. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of materialand a second device operative with said strip to provide a predeterminedtension in said strip between said first and second devices, thecombination of a motor member operatively connected to one of said firstand second devices for controlling the tension of said strip between thefirst and second devices to thereby control the thickness of said strip,a pressure control device for providing a first control signal thatvaries as a predetermined function of the pressure between said pair ofcooperating members, a first motor control device responsive to saidfirst control signal and operative with said motor member forcontrolling the tension of said strip between said first and seconddevices as a predetermined function of the variations of said firstcontrol signal, and a second motor control device responsive to saidfirst control signal for providing a second control signal which variesas a function of the magnitude of said first control signal, with saidsecond motor control device being operative with said motor member forcontrolling the tension of said strip between said first and seconddevices as a predetermined function of the variations of said secondcontrol signal.

3. In control apparatus for a rolling mill including a first devicehaving a pair of roller members operative with a strip of materialpositioned between said roller members, with said rolling mill includinga second device for pulling on the strip in a direction away from saidfirst device, the combination of a motor member operatively connected toone of said first devices and said second devices for controlling thetension of said strip between the first device and the second device, astrain measuring device operative with said first device for measuring apredetermined strain of said first device resulting from the operationof said roller members relative to said strip of material, with saidstrain measuring device providing a first control signal which varies asa predetermined function of said strain of said first device, a firstmotor control device responsive to said first control signal andoperatively connected to said motor member for controlling the tensionof said strip between said first device and said second device inaccordance with the variations of said first control signal, a secondmotor control device responsive to said first control signal forproviding a second control signal which varies as a pre determinedfunction of the variations of said first con trol signal, with saidfirst motor control device being responsive to said second controlsignal for controlling the tension of said strip between said firstdevice and said second device in accordance with the variations of saidsecond control signal.

4. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of materialand a second device operative with said strip to provide tension in saidstrip between said first and second devices, the combination of a motormember operatively connected to one of said first and second device forcontrolling the operation of said one device relative to said strip ofmaterial, a deformation sensing device operative with said first devicefor providing a first control signal that varies as a predeterminedfunction of' the deformation of said first device resulting from theoperation of said pair of cooperating members relative to said strip ofmaterial, a first motor control device responsive to said first controlsignal and operative with said motor member for controlling theoperation of said first device relative to said strip of material, and asecond motor control de vice responsive to said first control signal forproviding a second control signal which varies as a function of themagnitude of said first control signal, with said second motor controldevice being operative with said motor member for controlling theoperation of said first device relative to said strip of material as apredetermined function of the variations of said second control signal.

5. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of materialand a second de vice operative with said strip of material to provide atension in said strip between said first and second devices, thecombination of a pressure control device operative with said firstdevice for providing a first control signal that varies as apredetermined function of the pressure between said pair of cooperatingmembers, a reference control device for providing a second control.signal as a function of a predetermined desired pressure between saidpair of cooperating members, a first control device responsive to saidfirst control signal and responsive to said second control signal forcontrolling the operation of said first device in accordance with apredetermined comparison between said first control signal and saidsecond control signal for controlling the operation of said first devicerelative to said strip of material, and a second control deviceresponsive to said first control signal for providing a third controlsignal that varies as a predetermined function of said first controlsignal, with said second control device being operative with said firstdevice for controlling the operation of said first device relative tosaid strip of material as a predetermined function of the variations ofsaid third control signal.

6. In control apparatus for a rolling mill including a first devicehaving a pair of roller members between which a strip of material may bepositioned for performing a predetermined operation relative to saidstrip of material, said rolling mill including a second device forpulling on the strip relative to said first device, the combination of aroller pressure sensing device operative with said first device forproviding a first control signal that varies as a predetermined functionof the pressure between said pair of roller members, a motor operativewith one of said first and second devices, a first motor control deviceresponsive to said control signal and operatively connected to saidmotor for controlling the tension of said strip between said firstdevice andtsaid second device in accordance with the variations of saidfirst control signal, and a second motor control device responsive tosaid first control signal for providing a second control signal thatvaries .as a predetermined function of the variations of said firstcontrol signal, with said first motor control device being responsive tosaid second control signal for controlling the tension of said stripbetween said first device and said second device in accordance with thevariations of said second control signal.

7. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of material,with said control apparatus being operative with a second device toprovide a predetermined tension in said strip between said first andsecond devices, the combination of, a motor member operatively connectedto said first device for controlling the tension of said strip betweenthe first and second devices, a pressure control device operative withsaid first device for providing a first control signal that varies as apredetermined function of the pressure between said pair of cooperatingmembers, a first motor control device responsive to said first controlsignal and operative with said motor member for controlling the tensionof said strip between said first and second devices as a predeterminedfunction of the pressure between said pair of cooperating members, and asecond motor control device responsive to said first control signal forproviding a second control signal which varies as a function of saidfirst control signal, with said second motor control device beingoperative with said motor member for controlling the tension of saidstrip between said first and second devices as a predetermined functionof the pressure between said pair of cooperating members.

8. In control apparatus for a rolling mill including a first devicehaving a pair of roller members between which a strip of material may bepositioned for performing a predetermined operation relative to saidstrip of material, said rolling mill including a second device forpulling on the strip relative to said first device, the combination of aroller pressure sensing device for providing a first control signal thatvaries as a predetermined function of the pressure between said pair ofroller members, a motor operative with one of said first and seconddevices, a first motor control device responsive to said control signaland operatively connected to said motor for controlling the tension ofsaid strip between said first device and said second device inaccordance with the variations of said first control signal, a secondmotor control device responsive to said first control signal forproviding a second control signal that varies as a predeterminedfunction of the variations of said first control signal, with said firstmotor control device being responsive to said second control signal forcontrolling the tension of said strip between said first device and saidsecond device in accordance with the variations of said second controlsignal, and a strip tension limiting device operative with one of saidmotor control devices for limiting the strip tension between said firstand second devices to a predetermined maximum tension value.

9. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of materialand a second device operative with said strip to control the tension insaid strip between said first and second devices, the combination of amotor member operatively connected to one of said first device and saidsecond device for controlling the tension of said strip between thefirst and second devices, a pressure control device operative with saidfirst device for providing a first control signal that varies as apredetermined function of the pressure between said pair of cooperatingmembers, a first motor control device responsive to said first controlsignal and operative with said motor member for controlling the tensionof said strip between said first and second devices as a predeterminedfunction of said first control signal, a second motor control deviceresponsive to said first control signal for providing a second controlsignal which varies as a predetermined function of said first controlsignal, with said second motor control device being operative with saidmotor member for controlling the tension of said strip between saidfirst and second devices as a predetermined function of said secondcontrol signal, and a strip tension limiting device operative with saidmotor member for limiting to a predetermined maximum value the tensionof said strip between said first device and said second device.

10. In control apparatus for a first device having a pair of rollermembers and operative with a strip of ma- 13 terial for determining thethickness of said strip and a second device operative with said strip tocontrol the tension'in said strip between said first and second devices,the combination of a motor member operative with at least one of saidfirst and second devices for controlling the tension of said stripbetween said first and second devices, a roller pressure sensing devicefor providing a first control signal that varies as a predeterminedfunction of the pressure between said pair of roller members, with saidfirst control signal having one polarity when the pressure between saidpair of roller members is greater than a predetermined pressure and withsaid first control signal having an opposite polarity when the pressurebetween said pair of roller members is less than a predeterminedpressure, a first motor control device operative with said motor memberfor controlling the operating speed of said motor member, with saidfirst motor control device being responsive to said first control signalfor increasing the motor member speed when the first control signal hassaid one polarity and for decreasing the motor member speed when thefirst control signal has said opposite polarity, and a second motorcontrol device responsive to said first control signal for providing asecond control signal that has a first polarity when said first controlsignal has said one polarity and has a second polarity when said secondcontrol signal has said opposite polarity, with said second motorcontrol device being operative with said motor member to increase themotor member speed when said second control signal has said firstpolarity and being operative to decrease the motor member speed whensaid second control signal has said second polarity.

11. In control apparatus for a first device having a pair of rollermembers and operative with a strip of material for determining thethickness of said strip and a second-device operative with said strip tocontrol the tension in said strip between said first and second devices,thecombination of a motor member operative with at least one of saidfirst and second devices for controlling the tension of said stripbetween said first and second devices, a roller pressure sensing devicefor providing a first control signal that varies as a predeterminedfunction of the pressure between said pair of roller members, with saidfirst control signal having a first polarity when the pressure betweensaid pair of roller members is greater than a predetermined pressure andwith said first control signal having a second polarity when thepressure between said pair of roller members is less than apredetermined pressure, a first motor control device operative with saidmotor member for controlling the tension of said strip between saidfirst and second devices, with said first motor control device beingresponsive to said first control signal for increasing said striptension when the first control signal has said first polarity and fordecreasing said strip tension when the first control signal has saidsecond polarity, and a second motor control device responsive to saidfirst control signal for providing a second control signal that has afirst polarity when said first control signal has said first polarityand has a second polarity when said second control signal has saidsecond polarity, with said second motor control device being operativewith said motor member to increase said strip tension when said secondcontrol signal has said first polarity and being operative to decreasesaid strip tension when said second control signal has said secondpolarity.

12. In control apparatus for a first device having a pair of rollermembers and operative with a strip of material for determining thethickness of said strip and a second device operative with said strip tocontrol the tension in said strip between said first and second devices, the combination of a motor member operative with at least one ofsaid first and second devices for controlling the tension of said stripbetween said first and second devices, a roller pressure sensing devicefor providing a first control signal that varies as a predeterminedfunction of the pressure between said pair of roller members, with saidfirst control signal having a first polarity when the pressure betweensaid pair of roller members is greater than a predetermined referencepressure and with said first control signal having a second polaritywhen the pressure between said pair of roller members is less than apredetermined reference pressure, a first motor control device operativewith said motor member for controlling the operating speed of said motormember, with said first motor control device being responsive to saidfirst control signal for increasing the motor member speed when thefirst control signal has one of said first polarity and said secondpolarity and for decreasing the motor member speed when the firstcontrol signal has the other of said first polarity and said secondpolarity, and a second motor control device responsive to said firstcontrol signal for providing a second control signal that has a firstpolarity when said first control signal has said first polarity and ha asecond polarity when said second control signal has said secondpolarity, with said second motor control device being operative withsaid motor member to increase the motor member speed when said secondcontrol signal has one of said first polarity and said second. polarityand being operative to decrease the motor member speed when said secondcontrol signal has the other of said first polarity and said secondpolarity.

13. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of materialand a second device operative with said strip of material to provide atension in said strip between said first and second devices, thecombination of a pressure control device operative with said firstdevice for providing a first control signal that varies as apredetermined function of the pressure between said pair of cooperatingmembers, a reference control device for providing a sewnd control signalas a function of a predetermined desired pressure between said pair ofcooperating members, a first control device operative with one of saidfirst device and said second device and being responsive to said firstcontrol signal and responsive to said second control signal forcontrolling the operation of said one of said first and second devicesin accordance with a predetermined comparison between said first controlsignal and said second control signal for controlling the tension ofsaid strip between said first device and said second device, a secondcontrol device responsive to said first control signal for providing athird control signal that varies as a predetermined function of saidfirst control signal, with said second control device being operativewith one of said first device and said second device for controlling thetension of said strip of said first device relative to said strip ofmaterial as a predetermined function of said first control signal, withsaid first control signal being greater than said second control signalwhen the actual pressure between said pair of cooperating members isgreater than said predetermined desired pressure and with said firstcontrol signal being less than said second control signal when saidactual pressure between said pair of cooperating members is less thansaid predetermined desired pressure.

14. In control apparatus for a first device having a pair of cooperatingmembers between which a strip of material may be positioned forperforming a predetermined operation relative to said strip of materialand a second device operative with said strip of material to provide atension in said strip between said first and second devices, thecombination of a pressure control device operative with said firstdevice for providing a first control signal that varies as a function ofthe pressure between said pair of cooperating members, a refer- 15 encecontrol device. for providing a second control signal as a function of apredetermined desired pressure between said pair of cooperating members,a first control device operative with one of said first and seconddevices and responsive to said first control signal and responsive tosaid second control signal for controlling the operation of said one ofsaid first device and second device relative to said strip in accordancewith a predetermined comparison between said first control signal andsaid second control signal, a second control device responsive to saidfirst control signal for providing a third control signal that varies asa predetermined function of said first control signal, with said secondcontrol device being operaative with said first device for controllingthe operation 16 of said first device relative to said strip of materialas a function of said third control signal, and a strip tension limitingdevice operative with one of said control devices for limiting themagnitude of the total control signal applied to said first device.

References Cited in the file of this patent UNITED STATES PATENTS2,264,096 Mohler Nov. 25, 1941 2,281,083 Stoltz Apr. 28, 1942 2,322,418Crawford June 22, 1943 2,410,283 Gar Oct. 29, 1946 2,544,467 Michel Mar.6, 1951 2,659,154 Rendel Nov. 17, 1953

